Attosecond beats in sodium vapor

Transient time-delayed, four-wave mixing (TDFWM) experiments have been performed on the Na D doublet with use of a novel angled-beam geometry. The effects of PHz superposition-state modulations have been observed in the integrated TDFWM signal as a function of the time delay. As the time delay is varied, the lowest-order mixing signal modulates with a period of 980 asec - corresponding to the sum frequency of the two Na D lines. Higher-diffraction-order mixing signals contain modulation components at integral multiples of the doublet sum frequency. (Author)